Well, in a case of direct war with China or Russia, it will not be microchips you would be worried about.
USA is amazingly self sufficient nation, probably more than any other nation in the world, but... it lost far more critical items any nation must manufacture other than iphones.
You will not die from not receiving a new iphone, but you will die from lack of antibiotics if you catch gangrene, or something as dumb as typhus (my uncle died from it in his twenties)
USA can make a superweapons, but can't seem plainly make enough ammo for them. So much bad it is, a single German company produces more shells than entire American industry. All these big tanks, ships, and bombers will become useless in just 2-3 month of intense conflict.
After a big war, you will need huge amounts of basic materials to rebuild fast, before the enemy does the same. I have just to say: China has passed 1 gigaton of steel output per year